<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>rm是什么</title>
</head>
<body>
    <div class="parent">
       <div class="son">
        <div class="gson">

        </div>
       </div>
    </div>
</body>

<style>
    .parent{
        font-size: 30px;
    }

    .son{
        width: 300px;
        height: 300px;
        background-color: bisque;
        font-size: 11px;
    }
    
    .gson{
        width: 10em;
        height: 300px;
        background-color: black;
    }
</style>

</html>